In vacuum pumps of the regenerative type a rotor is mounted on a vertical shaft for rotation within a surrounding stator. The shaft is supported by upper and lower bearings which require lubrication. To facilitate lubrication of the upper bearing the shaft has a central axial bore and communicating radial holes in alignment with the upper bearing for delivering a lubricating fluid to the bearing.
A problem associated with lubricating the upper bearing is that it is frequently necessary to prevent or inhibit lubricating fluid from the upper bearing migrating in to the vacuum mechanism and hence in to the chamber being evacuated. To meet this problem it is known to create a barrier in the form of “clean” air.
In known systems either air or lubricating fluid in the form of oil may be delivered up the axial bore but not both. This results in either the air or the oil being delivered to the upper bearing by means externally of the shaft. If oil is delivered to the upper bearing via the axial bore of the shaft then significantly less power is consumed than using means, for example a pump external to the shaft since the centrifugal force generated by the spinning (rotating) shaft is utilised to drive the oil up the axial bore.
The purpose of delivering air to the upper bearing is to mix with the oil to create an oil mist for efficient lubrication but also, as aforesaid, to create a clean barrier to prevent or inhibit the migration of any oil from the upper bearing in to the vacuum mechanism. Thus the air at the upper bearing must not be contaminated with oil and since it is recirculated it must be demisted prior to arrival at the bearing. It is an advantage if the centrifugal force generated by the rotating shaft is utilised to provide a demisting effect on the air.
It is an object of the present invention to provide a system for lubricating the upper bearing supporting a rotating shaft forming part of a machine or pump which system allows both air and lubricating fluid to utilise the centrifugal effect of the rotating shaft.